Transcript Why direct measurements of the neutrino mass?

Double beta decay and Majorana neutrinos
Ettore Fiorini, Venice March 8, 2007
→
<=
→
=>
Majorana =>1937
Presently an essential problem in neutrino and
in astroparticle physiss
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The most sensitive way to investigate the Dirac or Majorana nature of the
neutrino is neutrinoless double beta decay (DBD)
This very rare process was sugested in general form by Maria Goepper Mayer
just one year after the Fermi theory of beta decay. Also Bruno Pontecorvo was
deeply involved.
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Double Beta –Disintegration
M.Goeppert-Mayer, The John Hopkins University
(Received May, 20 , 1935)
From the Fermi theory of b- disintegration the probability of
simultameous emission of two electrons (and two neutrinos) has been
calculated. The result is that this process occurs sufficiently rarely to allow
an half-life of over 1017 years for a nucleus, even if its isobar of atomic
number different by 2 were more stable by 20 times the electron mass
Double beta decay was at the beginning searched In the neutrinoless
channel as a powerful way to search for lepton number non
conservation. Presently it is also considered as the most powerful
way to investigate the value of the mass of a Majorana neutrino
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1. (A,Z) => (A,Z+2) + 2 e- + 2 ne¯
2. (A,Z) => (A,Z+2) + 2 e- + c ( …2,3 c)
3. (A,Z) => (A,Z+2) + 2 eProcess 1 has been detected in ten nuclei
Process2 and 3. violate the lepton number
Process 3, normally called neutrinoless DBD, would be revealed by
the presence of a peak in the sum of the electron energies => <mn>≠ 0
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u
d
d
e-
W
ne
W
ne
u
2n - bb decay
e-
d
u
W n
W
d
ee
ne
e-
u
0n - bb decay
Neutrinoless bb decay
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The rate of neutrinoless DBD strongly depends on the
evaluation of the nuclear matrix elements, quite
uncertain so far
rate of DDB-0n
Phase space
Nuclear matrix
elements
EffectiveMajorana
neutrino mass
1/t = G(Q,Z) |Mnucl|2 <mn>2
Need to search for neutrinoless DBD in various nuclei
A pick could be due to some unforeseen background peak
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Possible schemes for neutrino masses
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New calculations by.S.Pascoli and S.T.Petkov
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Experimental approaches
Geochemical experiments
i82Se
= > 82Kr, 96Zr = > 96Mo (?) , 128Te = > 128Xe (non confirmed), 130Te = > 130Te
Radiochemical experiments
238U = > 238Pu (non confirmed)
Direct experiments
Source = detector
(calorimetric)
e-
Source  detector
e-
detector
source
ee-
detector
Source  Detector
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heat bath
Cryogenic detectors
Thermal sensor
absorber
crystal
Incident
particle
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V
T 3
CV  1944 (
)( ) J/K
Vm D
2
E   k CVT
E
@ 5 keV ~100 mk ~ 1 mg
<1 eV
~ 3 eV
@ 2 MeV
~10 mk ~ 1 kg
<10 eV ~
keV
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Resolution of the 5x5x5 cm3
(~ 760 g ) crystals
:
@ 46 keV
@ 0.351 MeV
@ 0.911 MeV
@ 2.615 MeV
@ 5.407 MeV
210Po
a line
Counts
0.8 keV FWHM
1.4 keV FWHM
2.1 keV FWHM
2.6 keV FWHM
3.2 keV FWHM
(the best a spectrometer ever
realized)
Energy [keV]
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Present experimental situation
Technique
0n (y)
<mn)
scintillator
>1.4x1022
7-45
87
ionization
>1.9x1025
.12 - 1
2039
87
Ionization
>1.6x1025
.14 – 1.2
Klapdor et al 7.8
2039
87
ionization
1.2x1025
.44
82Se
NEMO 3
9.2
2995
97
tracking
>1.x1023
1.8-4.9
100Mo
NEMO 3
9.6
3034
95-99 tracking
>4.6x1023
.7-2.8
116Cd
Solotvina
7.5
3034
83
scintillator
>1.7x1023
1.7 - ?
128Te
Bernatovitz
34
2529
geochem
>7.7  1024 .1-4
130Te
Cuoricino
33.8
2529
bolometric
>2x1024
.16-.82.
136Xe
DAMA
8.9
2476
69
scintillator
>1.2x1024
1.1 -2.9
150Nd
Irvine
5.6
3367
91
tracking
>1.2x1021
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3-
Nucleus
Experiment
%
Qbb
48Ca
Elegant IV
0.19
4271
76Ge
HeidelbergMoscow
7.8
2039
76Ge
IGEX
7.8
76Ge
Enr
?
HM collaboration subset (KDHK):
claim of evidence of 0n-DBD
In December 2001, 4 authors (KDHK) of the HM collaboration announce the
discovery of neutrinoless DBD
t1/20n (y) = (0.8 – 18.3)  1025 y (1  1025 y b.v.)
Mbb = 0.05 - 0.84 eV (95% c.l.)
2004
2001
54.98 kg•y
2.2 s
skepticism in DBD community in 2001
71.7 kg•y
4s
better results in 200417
Two new experiments NEMO III and CUORICINO
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bb decay isotopes in NEMO-3 detector
bb2n measurement
116Cd
405 g
Qbb = 2805 keV
96Zr
9.4 g
Qbb = 3350 keV
150Nd
37.0 g
Qbb = 3367 keV
48Ca
7.0 g
Qbb = 4272 keV
130Te
454 g
Qbb = 2529 keV
100Mo
6.914 kg
Qbb = 3034 keV
82Se
0.932 kg
Qbb = 2995 keV
bb0n search
natTe
491 g
Cu
621 g
External
measure
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0n analysis
100Mo
 t1/20n (y) > 4.6  1023
82Se
 t1/20n (y) > 1.0  1023
Mbb < 0.7 – 2.8 eV
Mbb < 1.7 – 4.9 eV
(90% c.l.)
(90% c.l.)
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CUORICINO
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 Search for the 2b|on in 130Te (Q=2529 keV) and other rare events
 At Hall A in the Laboratori Nazionali del Gran Sasso (LNGS)
18 crystals 3x3x6 cm3 + 44 crystals 5x5x5 cm3 = 40.7 kg of
TeO2
Operation started in the beginning of 2003 => ~ 4 months
Background .18±.01 c /kev/ kg/ a
2 modules, 9 detector each,
crystal dimension 3x3x6 cm3
crystal mass 330 g
9 x 2 x 0.33 = 5.94 kg of TeO2
11 modules, 4 detector each,
crystal dimension 5x5x5 cm3
crystal mass 790 g
4 x 11 x 0.79 = 34.76 kg of TeO2 23
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Present CUORICINO result
anticoincidence spectrum
208Tl
line
(new)
detail
MT = 5.87 (kg 130Te) x y
b = 0.18  0.02 c/keV/kg/y
(Jul 2005)
60Co
pile-up
peak
DBD
130Te
DBD
Q-value
Energy [keV]
8.35 kg year of
130Te
<m0n> < .16 - .9 eV =>
t >3 x 1024 (90 % c.l.)
Klapdor et al m0n < .1- .9 eV
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DBD and Neutrino Masses
Present Cuoricino region
Arnaboldi et al., submitted to PRL, hep-ex/0501034
(2005).
Possible evidence
(best value 0.39 eV)
H.V. Klapdor-Kleingrothaus et al., Nucl.Instrum.and
Meth. ,522, 367 (2004).
With the same matrix elements the
Cuoricino limit is 0.53 eV
“quasi” degeneracy
m1 m2  m3
Inverse hierarchy
m212= m2atm
Direct hierarchy
m212= m2sol
Cosmological disfavoured
(WMAP) 26
region
Feruglio F. , Strumia A. , Vissani F. hep-ph/0201291
Next generation experiments
Name
%
Qbb
%E B
c/y
T (year)
Tech
<m>
CUORE
130Te
34
2533
90
3.5
1.8x1027
Bolometric
9-57
GERDA
76Ge
7.8
2039
90
3.85
2x1027
Ionization
29-94
Majorana
76Ge
7.8
2039
90
.6
4x1027
Ionization
21-67
GENIUS
76Ge
7.8
2039
90
.4
1x1028
Ionization
13-42
Supernemo
82Se
8.7
2995
90
1
21026
Tracking
54-167
EXO
136Xe
8.9
2476
65
.55
1.3x1028
Tracking
12-31
Moon-3
100Mo
9.6
3034
85
3.8
1.7x1027
Tracking
13-48
DCBA-2
150Nd
5.6
3367
80
1x1026
Tracking
16-22
Candles
48Ca
.19
4271
-
3x1027
Scintillation
29-54
CARVEL
48Ca
.19
4271
-
3x1027
Scintillation
50-94
GSO
160Gd
22
1730
-
1x1026
Scintillation
65-?
COBRA
115Cd
7.5
2805
Ionization
SNOLAB+
150Nd
5.6
3367
Scintillation
.35
200
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Ionization
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Ionization
COBRA
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C0BRA
Use large amount of
CdZnTe
Semiconductor Detectors
Array of 1cm3
CdTe detectors
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K. Zuber, Phys. Lett. B 519,1 (2001)
Scintillation
• 0n: 1000 events
per
• year with 1%
natural
• Nd-loaded liquid
• scintillator in
SNO++
Nd dissolved in SNO => tons of material;
by Alex Wright
simulation:
one year of data
maximum likelihood statistical test of the shape to extract
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0n and 2n components…~240 units of c2 significance after only 1 year!
Scintillation
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Tracking
SUPERNEMO
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Tracking
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EXO
concept: scale Gotthard experiment adding
Ba tagging to suppress background (136Xe
Present R&D
136Ba +2e)
■ Ba+ spectroscopy in HP Xe / Ba+ ex
■ single Ba detected by optical spectroscopy
■ energy resolution in LXe (ion.+scint.
■ two options with 63% enriched Xe
■ Prototype scale:
▶High pressure Xe TPC
► 200 kg enriched L136Xe without tagg
2P
▶LXe TPC + scintillation
1/2
650 nm
► all EXO functionality except Ba id
■ calorimetry + tracking
493 nm
► operate in WIPP for ~two years
■ expected bkg only by
-2
4D
3/2
■Protorype goals:
▶energy resolution E = 2%2
metastable
S1/2
►Test all technical aspects of EXO
47s
(except Ba id)
LXe TPC
►Measure 2n mode
►Set decent limit for 0n mode
(probe Heidelberg- Moscow)
■
Full scale experiment at WIPP or
SNOLAB
■10 t (for LXe ⇒ 3 m3)
▶b = 4×10-3 c/keV/ton/y
▶ 1/2
1.3×1028 y in 5 years
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▶〈m 〉
0.013 ÷ 0.037 eV
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CUORE expected sensitivity
In 5 years:
disfavoured by cosmology
b (counts/keV/kg/y)

[keV]
T1/2 [y]
<mn> [meV]
10-2
5
2.1 × 1026
19-100
10-3
5
6.5 × 1026
11-57
Strumia A. and Vissani F. hep-ph/0503246
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Other possible candidates for neutrinoless DBD
Compound
Isotopic abundance
Transition energy
48CaF
.0187 %
4272 keV
7.44 "
2038.7 "
4
9.63 "
3034
"
4
7.49 "
2804
"
34
2528
"
2
76Ge
100MoPbO
116CdWO
130TeO
150NdF
"
5.64 "
3
150NdGaO
2
3368“
3
130Te
has high transition energy and 34% isotopic abundance => enrichment
non needed and/or very cheap. Any future extensions are possible
Performance of CUORE, amply tested with CUORICINO
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How deep should we go?
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Total
Total Muon Flux v.s. Depth Relative to Flat Overburden
(cm-2 s-1)
Depth (km.w.e) Relative to Flat Overburden
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Neutron Flux at Underground Sites
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eg. Study for 60 kg Majorana Module
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CONCLUSIONS
Neutrino oscillations  m2 ≠0  <mn> finite for at leaqst one neutrino
Neutrinoless double beta decay would indicate if neutrino is a lepton violating
Majorana particle and would allow in this case to determine <mn> and the
hierachy of oscillations.
This process has been indicated by an experiment (Klapdor) with a value of
~0.44 eV but has not yet confirmed
Future experiments on neutrinoless double beta decay will allow to reach the
sensitivity predicted by oscillations
The multidisciplinarity of searches on double beta decay involves nuclear and
e subnuclear physics, astrophysics , radioactivity, material science,
geochronology etc. It could help in explaining the particle-antiparticle
asymmetry of the Universe
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